Mixer systems

ABSTRACT

A mixer system for aggressive (toxic, hazardous, corrosive, etc.) materials which are mixed (agitated, suspended, circulated, etc.) in a vessel with an impeller connected to a drive shaft has the impeller and its shaft mounted in an assembly which extends through an opening into the tank and closes that opening. The assembly has a cylindrical hub with a passageway through which the shaft extends out of an open end of the hub. Bearings which are made of materials resistant to the aggressive material in the tank are mounted in the hub and journal and support the shaft. The passageway is part of a confinement region which is terminated by a confinement shell which separates inner and outer rotors of a magnet coupling. The inner rotor is connected to the shaft, directly or through a gear train (preferably a planetary gear set). The outer rotor is connected to a drive shaft.

This Application is a Divisional of U.S. Ser. No. 08/024,715 now U.S.Pat. No. 5,368,390, filed Mar. 1, 1993.

DESCRIPTION

The present invention relates to mixer systems, by which is meantsystems for suspending, agitating and/or circulating materials,particularly liquids or liquid suspensions and particularly to mixersystems for mixing aggressive materials, by which is meant toxic,hazardous, corrosive or other materials which need to be confined forproper handling, processing or for environmental safety or healthreasons.

In order to prevent the escape of aggressive materials from the vesselin which they are mixed, confinement of the mixing apparatus whichcontacts the material has necessitated the use of magnet couplings whichprovide confinement shells or members or which use the wall of thevessel to separate the driven impeller apparatus from the motor andother drive elements. The spacing of the impeller and other parts of itsdrive apparatus, for example the impeller shaft, as well as the rotor ofthe magnet coupling with respect to the confinement shell or the otherseparating member (the wall of the tank) has necessitated the use ofbearings which control the run out of the shaft and the impeller so thatthere is no interference with the confinement shell or member. Theconventional approach has been to protect the bearings and to providedynamic, running seals which prevent the aggressive materials fromleaking into regions where the bearings are located. Such seals areundesirable since they have limited lifetimes and must be replacedbefore failure. The life of the seals is also subject to reductionbecause they are exposed to the aggressive material.

It is a feature of this invention to eliminate such seals therebyeffectively providing a sealless mixer system. Instead of resorting toseals, the bearings themselves are made, or at least surfaced, withmaterial resistant to the aggressive material being mixed. Theinvention, contrary to the conventional technology, uses bearings orjournals for the impeller shaft which are confined with the aggressivematerial. Notwithstanding, the conventional technology, it has beenfound in accordance with the invention that mixer systems havingacceptable lifetimes, in spite of their use with aggressive materials,are not only possible but practicable.

It is necessary in accordance with certain processing techniques, forexample when the aggressive material is altered from one type ofmaterial to another or has different ingredients thereto and proportionsare critical or the presence of materials previously being mixed isdetrimental to the process, that all or part of the region which isconfined be purged or even sterilized. In order to accommodate suchneeds, and in other applications where it is desirable to remove orreplace the bearings and other parts which are in confinement, a staticseal can be provided at a desired location and used when the impellershaft is stopped to isolate all or part of the region under confinement,for example the part containing the rotor and inside of the containmentshell of the magnetic coupling or even the aforementioned part includingthe bearings. It is a feature of the invention to provide in theimproved sealless mixer system an expandable collar which defines a sealagainst the shaft thereby isolating all or part of the region underconfinement and enabling it to be purged, say with nitrogen gas or evensterilized, as when the purging agent is steam. When the expandingcollar is in sealing relationship with the shaft, the shaft is stopped.During normal running conditions the collar does not interfere with theshaft and the sealless condition prevails.

The material which is subject to mixing may be under pressure and thevessel in which it is located is pressurized. This pressure may be usedin accordance with the feature of the invention to provide a secondaryor back up static seal in addition to the seal provided by theexpandable collar. Then a flange on the shaft and a collar confines aseal member (e.g., a O ring) between their opposed surfaces. The shaftmay be biased to separate the opposed surfaces so that under dynamicconditions when the shaft is rotating no seal is formed between theopposed surfaces. When the pressure is relieved, however, the bias iscounteracted by the pressure in the tank to enable the seal to be formedbetween the opposed surfaces thereby providing even further assurancethat the aggressive material will not escape from the vessel.

It is desirable for certain mixing applications that the impeller rotateat lower speed and provide higher torque than the motor which drives theimpeller. The magnet coupling has limited torque transfer capacity.Accordingly, mixing systems with magnetic couplings have been limited inthe amount of torque and mixing power which can be delivered to thematerial being processed. It is a feature of this invention to provide agear train in the confined region between the impeller shaft and theinside or inner rotor of the magnet coupling. Preferably the gear trainis provided by a planetary gear set thereby enabling the torque to bemultiplied in a volume which is available in the confined region.

It is the principal object of the present invention to provide improvedmixing apparatus, and particularly an improved mixer system which isadapted to be used for mixing aggressive materials.

A more specific object of the present invention is to provide animproved mixer system having one or more of the features discussedabove.

Briefly described, a mixer system embodying the invention is applicablefor mixing aggressive material in a vessel having an opening. A driveshaft for rotatably supporting a mixing impeller is used. The driveshaft is rotatably supported in bearings contained in an assembly whichis located in the opening and closes the opening to confine theaggressive material in the vessel. The assembly has an open passagewayin which the bearings and shaft are disposed. Since the passageway isopen, the mixer system is sealless. The passageway connects the bearingsand the vessel in communicating relationship for the aggressivematerial. There are no dynamic seals in the passageway. The bearingshave at least the surfaces thereof which are exposed to the aggressivematerial made of a material resistant to the aggressive material. Ifdesired, an expandable collar may be used to provide a static seal whenthe drive shaft is stopped. Passageways may be provided for releasingthe pressure behind the expanded collar in order to purge or sterilizethe parts of the assembly in confinement. For example the bearings maybe mounted in a cartridge which is removably disposed in the assembly.If torque multiplication is desired, the drive shaft may be connectedvia a gear train also in confinement. This gear train may be driven athigher speed and lower torque than desired to power the impeller througha magnet coupling; the gear train being connected to the inside part ofthe coupling. The term inner rotor should be taken to mean the insidepart of such a magnet coupling.

The foregoing and other objects, features and advantages of theinvention, as well as presently preferred embodiments thereof willbecome more apparent from a reading of the following description inconnection with the accompanying drawings in which:

FIG. 1 is a elevational view, partially in section, of a mixer systemembodying the invention;

FIG. 2 is an enlarged fragmentary elevational view of the region of themixer system of FIG. 1 which is in confinement and connected through asealless open end thereof to the mixing tank;

FIGS. 3, 4 and 5 are similar enlarged fragmentary elevational viewsshowing different arrangements of separator plates which mayalternatively be used in the assembly shown in FIGS. 1 and 2 to providestatic sealing and purging or sterilizing capabilities;

FIG. 6 is fragmentary elevational view similar to FIG. 2 showing theportion of the assembly which provides the confined region of the mixersystem, but in accordance with another embodiment of the invention.

FIG. 7 is a view similar to FIG. 6 which also shows the flange andpedestal and outer rotor drive but is in accordance with still anotherembodiment of the invention;

FIGS. 8 and 9 are respectively a view similar to FIG. 7, and anelevational sectional view 90° about the axis of the impeller driveshaft from the view shown in FIG. 8, both views showing a mixer systemin accordance with still another embodiment of the invention; and

FIGS. 10 and 11 are elevational views illustrating a mixer system whichenters the vessel or tank from the side (side entry) and which utilizesa planetary gear set, all in accordance with still another embodiment ofthe invention.

Referring to FIGS. 1 and 2, there is shown a top entry sealless mixersystem 10 which embodies the invention. Aggressive material to be mixedis introduced into a vessel 12 having its inside walls coated or madewith material which is resistant to the aggressive characteristics ofthe material. An impeller 14 is located in the vessel 12 and isconnected to a drive shaft 16. An assembly 18 has upper and lowerbearings 20 and 22 which rotatably support the shaft and also rotatablysupport an inner rotor 24 of a magnet coupling 26. This support isprovided by a cap nut 28 or bolt which is eccentrically disposed on theshaft 16 as shown in greater detail in FIG. 2, for torque transmission(acting like a cam) between the inner rotor 24 and the shaft 16.

The outer rotor 30 of the coupling 26 is connected via the flanged end32 of a shaft 34 which extends from a motor gear-box assembly 36. Themotor gear-box assembly is mounted on a bearing support 38 whichjournals the shaft 34. The magnet coupling 26 has circumferentiallydisposed arrays of permanent magnets in its inner and outer rotors 24and 30. The magnets in the inner rotor 28 are aligned with the magnetsin the outer rotor 30 but are polarized oppositely (i.e., north-south,south-north, north-south, south-north, etc.). The design of the coupling26 may be conventional and it may be of the type which is commerciallyavailable. The assembly 18 has a flange 40 which may be welded to a hub42 or may be one piece as shown in FIG. 2. The flange is bolted to aflange 44 of the nozzle 46 of the vessel 12 and closes the opening intothe vessel with the assembly 18. The motor 36 and its bearings support38 are mounted on the top of a pedestal 48 which has a lower end flange50 which is bolted to the flange 40. Openings 52 in the pedestal 48provide access to the internals of the mixer system (the bearing support38, the outer rotor 30 and the assembly 18). Ears 54 allow the mixerapparatus 10 to be lifted and transported. The ears are 120 degreesapart; thus only one ear appears in FIG. 1.

The assembly 18 also includes spacer plates 56 and 58 which areinterchangeable with static seal plates 60 and purge plates 62, as areshown and will be described in greater detail hereinafter in connectionwith FIGS. 3 and 5. These plates 56 and 58, either when used alone or indifferent arrangements with the plates 60 and 62, are bolted together bya circumferentially disposed array of bolts 64 to the flange 40. Themagnet coupling has a confinement shell (also known as a separator orseparating member) 66 having flange 68 which is bolted in the assemblyby the bolts 64. The shell 66 may also be called a containment shell.

The cylindrical hub 42 has an internal bore or passageway 70 whichdefines a passageway through which the shaft 16 extends and in which thebearings 20 and 22 are located. This passageway 70 is opened to thevessel 12 and therefore to the aggressive material confined thereinwhich, especially if the vessel is pressurized and the material canvaporize, is present in the passage 70. The passage 70 is part of aconfinement region which includes cylindrical bores in the plates 56 and58 and the inside of the confinement shell 66. The hub is terminated atits open end by an end cap 72 but is otherwise open and sealless.

The bearings 20 and 22 are bearings having rolling elements, namelyballs 74 and 76 and inner and outer races 78 and 80 for the bearing 20and 82 and 84 for the bearing 22. The bearings are axially spaced fromeach other, with the bearing 82 closer to the open end 71 of thepassageway 70 and the bearing 20 further from the open end 71, by spacersleeves 86 and 88. The shaft 16 has a shoulder 90 which references theinner race 82. The inner race and the bearing 22 is fixed in axialposition by the spacer sleeve 86 which sandwiches the inner race 78 ofthe bearing 20 and is compressed against that inner race by forceapplied from the bolt or nut 28 against the upper end of the spacersleeve 88 via a shoulder 92 which extends downwardly from the hub 94 ofthe inner rotor 24. The outer race 84 is fixed between a step 96 aroundthe bore 70 and a shoulder 98 of the end cap 72. The outer race 80floats axially in the bore to take up thermal expansion and tolerancesin manufacture.

The balls 74 and 76 of the ball bearings and the races thereof are allexposed to the aggressive material. The surfaces which are exposed aremade of material resistant to the aggressive material. Desirably theballs are made of entirely such material so that their surfaces areresistant. The balls may be a ceramic, for example silicon nitride. Analternative material which may be suitable for other applications isstellite. Stellite is a boron containing alloy. It has been found thatstellite, sold under the tradename Hanes 25 is suitable. (The races maybe stellite of Rockwell C hardness of about 60). For some applications,steel races having a zirconium/zirconium nitride vapor deposition orsputtered coating may be used. For other applications the races may beplated with thin dense chromium, for example a 0.3 mil coating ofchromium. Other types of coatings may be applied by vapor deposition orsputtering. The thin dense chromium material is sold under the tradenameArmalloy. Other materials which are resistant or more preferably inertto the aggressive material being mixed may be used.

FIGS. 3 and 5 illustrate a static seal which may be provided by apneumatically pressurized collar 100 of elastomeric material, forexample, such as viton, a elastomeric polymer. The collar is a hollowannulus on a ring shaped metal core 102. Such expandable seals arecommercially available. Pressurized air is introduced through a port 104into a ring 106 which communicates with the front end of the corethrough holes 108. Normally the collar does not interfere with the shaftnor contact the sleeve 88. The collar is expanded only when the motorand the shaft 16 are stopped. Then access may be had to the magnetcoupling. A normally plugged opening may be provided in the purge ringof plate 56 to relieve the pressure between the expandable collar andthe confinement shell. By locating the collar 100 above the hub andabove the bearings 20 and 22, the bearings and the passageway 70 remainexposed to the aggressive material.

As shown in FIG. 5 the purge plate 62 has a port 108, an annularmanifold 110 and a plurality of circumferentially disposed openings 112.The purge plate may have the port 108 plugged and then opened to relievethe pressure behind the expanded collar 102. Alternatively, inert gas,such as nitrogen or sterilizing vapors, such as steam, may be introducedthrough the port 108, the manifold 110 and the openings 112 to purgeand/or sterilize the confinement region above the collar 102.

In the event that purging into the vessel 12 is desired only the ringplate 58 is used together with the purge plate 62 as shown in FIG. 4.Then the vessel 12 as well as the passageway and the entire confinementregion can be purged and/or sterilized. The exhaust from the vessel maybe by suction applied to the port 108 of the purge plate 62 or via anopening (e.g., the fill opening) in the tank or vessel 12.

Referring to FIG. 6 there is shown an assembly 120 using a hub 122 andflange 124 connectable to an opening (nozzle) of a tank, such as shownin FIG. 1, for closing that opening. The hub 122 receives the bearings20 and 22 in a cartridge 126. The cartridge is a cylindrical tube havingsteps 130 and 132 against which the outer races of the bearings 20 and22 are referenced and held in place by snap rings 134 and 136. The upperbearing 20 is fixed since its inner race is referenced against a step138 on the shaft and held against that step 138 by a tubular sleeve 141which may be compressed by the hub shoulder of the inner rotor asdiscussed in connection with FIGS. 1 and 2. The inner race of the lowerbearing 22 is allowed to float. The bearings 20 and 22 may be made ofmaterials similar to those discussed above.

Below the bearings, in a ring plate 140 which is sandwiched against thebottom end of the hub 122 by a grooved end cap 142, is an expandablecollar 144. A split collar or neck 146 which is clamped to the shaft andlocated in the grooved end cap 142 provides shoulders to limit the axialmovement of the shaft, particularly the downward movement of the shaftinto the tank 12.

Since the expandable collar 144 is disposed at the bottom of thepassageway defined in the cartridge 126 around the shaft and thenupwardly into the confinement region which is closed by the confinementshell 66, substantially the entire confined region in the assembly 120may be statically sealed.

A purge plate 150 is sandwiched between the flange 68 of the confinementor containment shell and the hub 122 at the upper end thereof. Thisplate has normally plugged inlet and outlet ports 152 and 154 to whichholes 156 and 158 extend. When the plugged port 154 is opened theconfined region may be depressurized. The confined region may be purgedor sterilized by introducing gas or sterilizing vapors through the inletport 152 and exhausting the gas or vapors (e.g., nitrogen and/or steam)through the outlet port 154.

The expandable collar 144 is connected via a passage 160 for pressurizedair or gas to a control line from a pump (not shown). The bore in thehub in which the cartridge 126 is disposed may have an annular groove orrelief 162 which facilitates the insertion and removal of the cartridge126 and decreases the area of the bore in the hub 122 and the outside ofthe cartridge 126 which needs to be precisely machined.

FIG. 7 illustrates an assembly 170 with a hub 172 and a cartridge 174carrying bearings 178 and 180. The bearings 178 and 180 may respectivelyfloat downwardly and upwardly on the shaft at their inside races. Theoutside races of the bearings are both fixed by spacers and snap rings.Passages 184 and 186 bypass the bearings 178 and 180.

The mixer shown in FIG. 7 has a magnet coupling 188 with outer and innerrotors 190 and 192 separated by a confinement shell 194. This couplingmay be somewhat different in design from the coupling 26, but isfunctionally identical therewith. The inner rotor 192 is connected tothe shaft 182 by a cap nut 196 which holds the hub of the rotor 192against a spacer sleeve 198 which acts as a shoulder against the innerrace of the bearing 178.

The shaft 182 has a flange 200 which extends radially into a groovedefined by the lower surface of a pneumatically pressurized collar 202and an end cap 204. This groove also captures an expandable elastomericcollar 206 which is normally clear of the flange 200, but when expandedby compressed air which extends to the collar through a line (not shown)defines a seal against the circumferential rim 208 of the flange 200.The flange 200 has a groove which locates an O-ring seal member 210. Thegap between the opposed surfaces of the flange 200 and the collar 202where the O-ring 210 is located is spaced apart sufficiently to preventa seal from being formed by the O-ring during normal running operationof the shaft. This is because the shaft is biased downwardly by a wavespring 212 (an annular spring member) which is captured between the foot214 of the confinement shell 194 and the top of the hub 172 and extendsradially inward. The bias of this spring is transferred through a ringshaped plate 216 which is bolted to the top of the cartridge 174. Theforce then is transferred via the lower bearing 180 to the shaft 182 ina downward direction thereby creating the gap of sufficient size toprevent the formation of the seal by the O-ring 210.

When the collar 206 is expanded and a port 218 which extends via aconduit 220 in the hub through the collar 202 is opened, the flange 202,acting as a piston, counteracts the bias of the wave spring 212 andenables the seal to be formed by the O-ring 210. The O-ring thereforeprovides a double or secondary seal in addition to the expandable collar206. The flange 200 provides a stop when it engages the end cap 204.

The bypasses around the bearings 178 and 180 assure that the pressure inthe confined region is relieved when the port 218 is opened. The port218 may also be used for purging, sterilizing, etc. when the staticseals are in place.

FIGS. 8 and 9 show a mixer system 230 which is similar in design to theembodiment shown in FIG. 7 except that sleeve bearings instead of ballbearings are used. There are upper and lower sleeve or journal bearings232 and 234 and thrust bearings 238. These thrust bearings are plates onopposite sides of a web 240 or flange which is appertured, like thejournal bearings 232 and 234 at holes 242 and 244 so as to bring allparts of the confined region into communicating relationship. The thrustbearings 238 are pressed into the cartridge 174 and a cap 246 whichholds the upper pad of the thrust bearing 238 in place. The wave spring212 bears against this cap 246 to open the gap where the O-ring 210 islocated during normal running operation. When the pneumaticallypressurized collar seal is formed by air pressure applied to lines 248and 250 and the pressure behind the piston 200 is released via theconduit 220 and the plug 218, the spring 212 is further compressed,counteracting its bias by the pressure in the vessel and enabling theseal to be formed by the O-ring 210. The journal and thrust bearings maybe of material resistant or inert to the aggressive material beingmixed. A sintered graphite material (e.g. Graphalloy) or a polyamidimid(e.g. Vespel) are suitable. for this purpose.

FIGS. 10 and 11 show a side entry mixer 260 which enters through theside wall 262 of a tank 264. The side wall has a flange nozzle 266 whichforms the opening into the tank. This nozzle is sealed by the assembly268 including ball bearings 270 and 272 in a cartridge 274 in the boreof a hub 276. The hub is sealless and has an open end which may have abushing 278. This bushing does not form a seal so that the mixer 268 issealless as was the case with the mixer system described above.

The mixer 268 has an impeller 280 and an impeller shaft 282 which isjournaled in the bearings 270 and 272. The shaft has a flange 284,against the rim of which an expandable collar 286 may be expanded toform a static seal. A double seal is not used in this embodiment of theinvention. Pressurized air to the collar 286 is applied via a conduit288.

The impeller shaft 282 is connected to a gear box 290 containing a geartrain in the form of a planetary gear set 292. This gear train as wellas the passageway in the cartridge 274 which carries the bearings 270and 272 are contained in the gear train housing 290.

The gear train is driven by a shaft 294 which is connected to the innerrotor 296 of a magnet coupling 298 by a shaft 300 connected to a motor302 via an adapter 304. The magnet coupling 298 has an outer rotor 306which is connected to the shaft 300. The motor 302 is supported on atable 306. The motor front end is mounted on a pedestal 308 which isbolted to a flange 310 which extends radially from the hub 276 of theassembly 268. The flange and pedestal are bolted to the nozzle flange266.

The planetary gear set 292 has a sun gear 310 which engages planet gears312 mounted on roller bearings to a planet carrier 314. The planet gearsengage a ring gear 315 which is mounted on the housing 290. The outputof the planetary gear set 292 is taken at an adapter 316 connected tothe upper end of the impeller shaft 282 by one or more splines 320. Theplanet gear is continuously lubricated by oil in the housing which iscirculated by blades 322 on a sleeve 324 connected to the shaft 294 asby a set screw. The oil circulates through ball bearings 326 and 332which support the shaft 294 against thrust and radial movement andthence through the planet gears 312 and the sun gear to a splash guard328. There are holes 330 for the circulation of oil backward to anotherbearing 332, the sleeve 324 and back to the bearing 326 and theplanetary gear set 292. The oil may be admitted into the housing 290 viaa top plug 334 and drained via a drain plug 336.

Planet gear set 292 provides a reduction in shaft speed andmultiplication in torque delivered to the impeller shaft 282. Ifadditional speed reduction and torque multiplication is desired anotherplanetary gear set may be mounted in series and coaxially with the gearset 292 shown in FIG. 11. In the event that the tank 264 contains oil orother lubricating material which does not interact with the oil in theconfinement region of the assembly, then it may be desirable to fill theconfinement region with oil and to arrange conduits and a piston toequalize the pressure in the confinement region of the assembly 288 withthe pressure in the tank thereby preventing leakage into the tank of theoil in the confinement region or leakage of oil from the tank into theconfinement region. The planet gear set may be dry running, and the useof such dry running gears may be preferred, especially in the top entrymixer systems, such as shown in FIGS. 1-9.

From the foregoing description it will be apparent that there has beenprovided improved mixer systems, and especially systems using magnetcouplings and sealless entry into a vessel in which mixing occurs.Variations and modifications of the herein described mixer system, inaccordance with the invention, will undoubtedly suggest themselves tothose skilled in this art. According the foregoing description should betaken as illustrative and not in a limiting sense.

We claim:
 1. A mixer system which comprises an impeller having a shaftadapted to be driven by a motor at a lower speed and with higher torquethan delivered by said motor, a magnet coupling having an inner rotorand an outer rotor, said outer rotor being connected in drivingrelationship with said motor, a member disposed between said inner andouter rotors for separating said inner rotor and said shaft and saidimpeller from said outer rotor and said motor, and a reduction geartrain connected between said inner rotor and said impeller shaft forrotation at lower speed and higher torque than said motor and beingseparated by said separating member from said outer rotor and saidmotor.
 2. The mixer system according to claim 1 wherein said reductiongear train is a planetary gear set having a sun gear connected to saidinner rotor and planet gears in a carrier connected to said impellershaft.
 3. The mixer system according to claim 2 wherein said planetarygear set is dry running.